Colloidal solution of silver nanoparticles and method of it preparation

ABSTRACT

The invention relates to colloidal solutions of silver nanoparticles and to method of it preparation and can be used in different areas, particularly in medicine, veterinary science, food industry, cosmetology, household chemistry and agrochemistry. Method includes the electrochemical dissolution of silver in the deionized water. The silver in fine powder form with chemical purity of 99.999% and with nanoparticle sizes up to 100 nm is subjected to electrochemical dissolution in electrolyser, within which are located the electrodes in form of containers made from chemically neutral material, in which fine powder of silver from 100 to 150 g are placed, and by means of conductor covered by chemically neutral coat the direct voltage ranges from 30 to 45 volts is energized. Electrolysis is proceeded under conditions of cycling voltage polarity every 2 hours and mechanical stirring of solution 2 times in twenty-four hours until the concentration of silver in colloidal solution from 5.0 to 100 mg/l. Wherein the portion of silver metal nanoparticles is from 5 to 90% of total concentration of silver in solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of total volume of silver metal nanoparticles in solution, the portion of nanoparticles ranging from 15 to 35 nm is correspondingly from 15 to 35%, the residual portion of total silver concentration in solution is silver ions. The technical result of invention is preparation of the stable colloidal solution of silver nanoparticles.

TECHNICAL FIELD

The invention relates to inorganic chemistry, mainly to colloidal solutions of silver nanoparticles and to method of it preparation and can be used in different areas, particularly in medicine, veterinary science, food industry, cosmetology, household chemistry and agrochemistry.

BACKGROUND ART

For purposes of the clarity of the description some term definitions are given in the invention.

The term <<deionized water>> means water without impurities. The resistivity of such water is up to 18 MOhm·cm, the purity is 99.999%.

Ion-monatomic or polyatomic electrically charge particle, forming consequently of loss or attaching one or several electrons by atom or molecule.

The term <<silver noble metals>> relates to the metals of VIII group of Periodical System.

Silver nanoparticles ranging 1-100 nm can be obtained in different geometrical forms. This small particles comprise metal-element in chemically reduced form and, depends on method of theirs preparation can be stored both in form of reduced solid powders and in form of stable suspension in solvents, for example, in water or alcohol (in form of colloids or soles).

The term <<colloid>> relates to fluid composition of microscopic particles suspended in liquid medium (soles). In typical colloids said particles have size in range from 1 nm to 1 micrometer (from 10⁻⁷ to 10⁻⁵ cm). In transparent colloids dispersion of light ray is observed (Tyndall effect). Disperse particles are not precipitated at the expense of Brownian motion.

Colloidal solutions of silver (i.e. stable system of <<silver nanoperticles-solvent>>) are painted, this is physical property of silver nanoparticles, wherein color depends on size of particles, and <<purity>> of color depends on homogeneity of particles according to the sizes.

It is typically for colloids that they are stable in water solution only if their aggregation is prevented, for example, by means of stabilizing factors.

Stabilization of colloidal solutions can be made by adding small quantity of high-molecular substances that are adsorbed on the particle surfaces and prevented theirs aggregation.

It is known the method of preparation of stabilized colloid (EP patent No. 2007513), comprising the steps of heating of water up to fist state temperature, adding into water silver nitrate, heating the mixture up to second required temperature, adding into mixture lithium citrate followed by heating up to required temperature, cooling mixture.

It should be noted that colloid prepared by method described in EP patent No. 2007513 can be used mainly in Raman spectroscopy.

It is known the method of preparation of silver nanoparticles in liquid medium (RU patent No. 230344) providing high stability and comprising the steps of solution of stabilizers in distilled water under stirring, immersing anode made in form of silver plate into finished solution, and cathode made in form of stainless steel plate, electrochemical dissolution of anode under passing the constant regulated current through the solution. The method described in RU patent No. 2390344 provide high stability of resulted silver nanoparticles at the expense of stabilizers.

The silver nanoparticles obtained by the method, described in the RU patent No. 2390344, is intended to use for the production of medical, veterinary and cosmetic preparations.

Thus, the described above technical decisions assisting of stabilization of colloids are based on the processes, whereby the colloids were formed due to the previous reaction.

The closest to the proposed invention on the basis of the group of essential note and object matter is O.V. MOSIN “Product of nanotechnology—colloidal silver” on the site (http://www.sciteclibrary.ru/rus/catalog/pages/9151.html, page 1, 9-10, published Jul. 7, 2008), in which the method of preparation of the colloidal solution of silver nanoparticles is presented, comprising electrochemical dissolution of silver in the deionized water, and it is also presented the colloidal solution of silver nanoparticles, comprising the deionized water, the silver metal nanoparticles, and the silver ions.

An object of the claimed invention is preparation the stable colloidal solution of silver nanoparticles by the method not allowing the aggregation of the silver metal nanoparticles without using of stabilizers.

The technical result of the claimed invention accomplishing under use of invention is preparation of stable colloidal solution of silver metal nanoparticles by the proposed method, in which the size of silver metal nanoparticles and respectively the weight of silver metal nanoparticles are such, that the mutual repulsive force of unipolar dipoles of water surrounding the silver metal nanoparticles is higher than gravitational forces acting on these particles, wherewith the keeping of silver metal nanoparticles in uniformly suspension and in the equal concentration throughout the volume of solution occurs.

For solving the object of the invention and achieving technical result indicated above the group of the inventions united under general inventor conception is proposed.

The one of the subject of the proposed invention is method of preparation of colloidal solutions of silver nanoparticles, comprising an electrochemical dissolution of silver in deionised water, characterized in that, silver in fine powder form with chemical purity of 99.999% and with nanoparticle sizes up to 100 nm is subjected to electrochemical dissolution in electrolyser, comprising housing made from chemically neutral material, within which are located the electrodes in form of containers made from chemically neutral material, in which fine powder of silver from 100 to 150 g are placed, and by means of conductor covered by chemically neutral coat the direct voltage ranges from 30 to 45 volts is energized by means of dc power source under conditions of cycling voltage polarity every 2 hours and mechanical stirring of solution 2 times in twenty-four hours until the concentration of silver in colloidal solution from 5.0 to 100 mg/l, wherein the portion of silver metal nanoparticles is from 5 to 90% of total concentration of silver in solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of total volume of silver metal nanoparticles in solution, the portion of nanoparticles ranging from 15 to 35 nm is correspondingly from 15 to 35%, the residual portion of total silver concentration in solution is silver ions.

According to method the mechanical stirring of solution is performed by the use of solution contact means made from chemically neutral material.

According to method the energizing of the voltage on the silver in form of fine powder is performed by the use of conductors covered by chemically neutral coat and passed into electrolyser.

According to method the additionally filtering of colloidal solution is performed.

The another subject of the proposed invention is colloidal solution of silver nanoparticles, characterized in that, it comprise deionized water, silver metal nanoparticles and have silver concentration from 5.0 to 100 mg/l, wherein the portion of silver metal nanoparticles is from 5 to 90% of total concentration of silver in solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of total volume of silver metal nanoparticles in solution, the portion of nanoparticles ranging from 15 to 35 nm is correspondingly from 15 to 35%, the residual portion of total silver concentration in solution is silver ions.

According to the invention the colloidal solution of silver nanoparticles is stable during at least two years.

It should be noted that in the general concentration of silver in the solution the portion of silver metal nanoparticles is from 5 to 90% depending on tasks (sphere of the use of the finished product).

During the research process were selected the parameters of the method of preparation of the colloidal solution of silver nanoparticles on the basis of the electrolysis rate and the time of process, which is directly proportional to the volume of electrolyzer and to a quantity of fine dispersed powder of silver placed into the electrolyzer, and is inversely proportional—to voltage supplied to the electrodes. It was also established that sizes of silver nanoparticles in the solution and their quantity with respect to silver ions are in direct dependence from the frequency of the change of polarity and from the frequency of mechanical stirring. It is important to note that according to the results of performed investigations the obtained colloidal solution of silver nanoparticles keeps stability during, at least, two years without the addition of stabilizing chemical, biological and other components, and without the physical stabilization.

It should be noted that filtration of colloidal solution of silver nanoparticles additionally is performed for preparation of colloidal solution of silver nanoparticles with given concentration. The step of filtration can be performed, if it is necessary to obtain solution with the given size of particles (for example, not more than 10 nm).

Invention is illustrated by an example of the method of preparation of colloidal solution of silver nanoparticles.

BEST MODE FOR CARRYING OUT THE INVENTION

Example of the method of preparation of the stable colloidal solution of silver nanoparticles.

In the process of preparation of colloidal solution of silver nanoparticles is used: the deionized water obtained by the multistage filtration after which the conductivity of purified water must be not more than 0.3 mS/Sm (microsiemens/centimeter); to electrochemical dissolution is subjected silver in the form of fine dispersed powder with chemical purity of 99.999% and sizes of the particles of the powder up to 100 nm.

The deionized water is moved into the electrolyzes made in the form of the capacity having a volume of 5 liters and more (20 liters), from the chemically neutral material (for example, chemically neutral glass—NC-3, polyethylene of high pressure, fluorocarbon polymer).

For the protection of the entry of dust and other small particles on top the capacity is capped. Inside the housing are located the containers, made from chemically neutral material, in which fine powder of silver from 100 to 150 g are placed (to the volume of the electrolyzes of 20 liters). Containers with fine powder are electrodes. Constant voltage in the optimum (experimentally established) range from 30 to 45 volts by means of the source of power of direct current is supplied to the electrodes by means of the conductor covered by chemically neutral coat. The change of polarity is produced with the periodicity 2 hours. Stirring of solution is achieved by a mechanical method (for example, with the use of a peristaltic pump and hoses lowered in the electrolyzer in the opposite angles at different depth) periodically 2 times in twenty-four hour period for preventing the formation of large particles in the space between the containers with silver and for the purpose of preventing obtaining ionic solution.

As a result is obtained the colloidal solution of silver nanoparticles with total concentration of silver in the ranges from 5.0 mG/l (lower than said value—not to measure) to 100.0 mG/l (higher than the said value—not to obtain because of the aggregation of particles).

In the obtained colloidal solution the portion of the silver metal nanoparticles is from 5 to 90% of the total concentration of silver in the solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of the total volume of the silver metal nanoparticles in the solution, the portion of nanoparticles ranging from 15 to 35 nm is respectively from 15 to 35%, the residual portion of total concentration of silver in the solution is silver ions, which is confirmed by the performed laboratory researches. Namely, the total concentration of silver in the solution was determined by the method of mass-spectroscopy (by means of the atomic-emissive spectrograph with the inductively coupled plasma—ICP OES). Ion concentration of silver in the solution was determined by means of the ion-selective electrodes. The concentration of the silver metal nanoparticle in the solution and their size distribution were determined by means of an instrument of Zetasizer Nano of the company Malvern.

Obtained by this method colloidal solution of silver is transparent. The absence of color is the indirect confirmation of the fact that a basic quantity of nanoparticles in the volume of solution has a size of less than 15 nm.

For preparation of the colloidal solution of silver nanoparticles with given size of particles (for example, not more than 10 nm) is performed it filtration. Filtration performed by means of sterile micro-filters with given selectivity according to the size of the passed particles, for example, MILLEX GP of firm Millipore.

The obtained colloidal solution of silver nanoparticles is poured into the storage capacity. Solution is subject to storage at room temperature both in the presence of ultraviolet radiation and in the darkness without the aggregation during, at least, the 2 years (according to the results of the experiments, carried out by FGUN <<The institute of the toxicology>> of FMBA of Russia). The colloidal solution of silver nanoparticles save stability (according to the results of the experiments, carried out by FGUN <<The institute of the toxicology>> of FMBA of Russia) during, at least, the 2 years without the addition of stabilizing chemical, biological and other components and physical stabilization.

Freezing the colloidal solution of silver nanoparticles (to the complete solid aggregative state) and its subsequent thawing, (as shows the results of the carried out experiments in FGUN <<The institute of the toxicology>> of FMBA of Russia) does not affect the stability of solution, and it does not change its properties.

Thus, the example, which illustrates invention, clearly confirms that under specific parameters of method procedure selected during the research is performed the stable colloidal solution of silver nanoparticles, in which the sizes and the properties of the surface of forming silver nanoparticles prevent subsequently of their coagulation. The performed by the proposed method colloidal solution of silver nanoparticles can be used in medicine, veterinary science, cosmetilogy, household chemistry and agrochemistry, and also in the food industry. 

1. Method of preparation of colloidal solutions of silver nanoparticles, comprising an electrochemical dissolution of silver in deionized water, characterized in that, silver in fine dispersed powder form with chemical purity of 99.999% and with nanoparticle sizes up to 100 nm is subjected to electrochemical dissolution in electrolyser, comprising housing made from chemically neutral material, within which are located the electrodes in form of containers made from chemically neutral material, in which fine powder of silver from 100 to 150 g are placed, and by means of conductor covered by chemically neutral coat the direct voltage ranges from 30 to 45 volts is energized by means of dc power source under conditions of cycling voltage polarity every 2 hours and mechanical stirring of solution 2 times in twenty-four hours until the concentration of silver in colloidal solution from 5.0 to 100 mg/l, wherein the portion of silver metal nanoparticles is from 5 to 90% of total concentration of silver in solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of total volume of silver metal nanoparticles in solution, the portion of nanoparticles ranging from 15 to 35 nm is correspondingly from 15 to 35%, the residual portion of total silver concentration in solution is silver ions.
 2. The method according to claim 1, characterized in that, mechanical stirring of solution is performed by the use of solution contact means made from chemically neutral material.
 3. Method according to claim 1, characterized in that, energizing of the voltage on the silver in form of fine powder is performed by the use of conductors covered by chemically neutral coat and passed into electrolyser.
 4. Method according to claim 1, characterized in that, additionally filtering of colloidal solution is performed.
 5. Colloidal solution of silver nanoparticles, characterized in that, it comprise deionized water, silver metal nanoparticles and have silver concentration from 5.0 to 100 mg/l, wherein portion of silver metal nanoparticles is from 5 to 90% of total concentration of silver in solution, the portion of nanoparticles ranging from 2 to 15 nm is from 65 to 85% of total volume of silver metal nanoparticles in solution, the portion of nanoparticles ranging from 15 to 35 nm is correspondingly from 15 to 35%, the residual portion of total silver concentration in solution is silver ions.
 6. Colloidal solution of silver nanoparticles according to claim 5, characterized in that, it is stable during at least two years. 